JP2592432B2 - Evaporative fuel control system for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel vapor control system for an internal combustion engine having a fuel vapor emission control device.

[0002]

2. Description of the Related Art Heretofore, a fuel vapor emission suppression device for preventing fuel vapor generated from fuel in a fuel tank from being released into the atmosphere has been widely used. In this device, fuel vapor is temporarily stored in a canister, and the stored fuel vapor is supplied to an intake system of an internal combustion engine. By supplying (purging) the fuel vapor to the intake system,
Because the air-fuel ratio of the mixture supplied to the engine fluctuates,
When the supply of fuel vapor to the intake system is started (at the transition from the stop of the purge to the execution of the purge) and at the time of the stop of the supply (at the transition from the execution of the purge to the stop of the purge), the opening of the control valve for controlling the supply is changed. A purge control method of gradually changing the purge control has been known (Japanese Patent Publication No. 63-97787).
No.).

[0003]

According to the above conventional method, at the time of the transition from the stop of the purge to the execution, even if the concentration of the fuel vapor in the air-fuel mixture supplied to the intake system is low, the mixing is stopped. Since the flow of air will gradually increase,
Only a purging amount smaller than the purging amount can be performed, and the processing capability of the fuel vapor emission suppression device cannot be sufficiently exhibited.

Further, at the time of transition from the execution of the purge to the stop, there is a problem that if the opening of the purge control valve is gradually reduced, HC and CO in the exhaust gas increase.

The present invention has been made in view of the above points, and appropriately controls the opening of the purge control valve at the time of transition from stoppage of purge to execution or vice versa. It is an object of the present invention to provide an evaporative fuel control device capable of sufficiently exerting its performance and improving exhaust gas characteristics.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for purging an air-fuel mixture containing a fuel vapor provided between a canister for adsorbing fuel vapor generated from a fuel tank and an engine intake system. In an evaporative fuel control apparatus for an internal combustion engine having a purge passage through which a purge gas is supplied and a purge control valve which controls a flow rate of fuel vapor supplied to an engine intake system through the purge passage, the amount of opening of the purge control valve is increased or decreased. And purge storage means for storing control parameter values of the purge control valve, and purge start means for setting the stored control parameter values as initial values at the start of purge supply from a purge stop state. It is provided.

In addition, instead of or in addition to the purge start means, a purge stop means for immediately setting the control parameter value to a value corresponding to the valve closed state when shifting from the purge supply state to the purge stop state is provided. It was made.

[0008]

In the transition from the stop of the purge to the execution, the control parameter value stored in the storage means is used as an initial value, and the purge control valve is immediately opened to the opening corresponding to the initial value.

At the time of transition from the execution of the purge to the stop, the purge control valve immediately closes to the fully closed state.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is an overall configuration diagram of an internal combustion engine and a fuel supply control device therefor according to an embodiment of the present invention. Reference numeral 1 denotes, for example, a four-cylinder internal combustion engine.
A throttle body 3 is provided in the middle of the intake pipe 2.
A throttle valve 301 is provided therein. The throttle valve 301 has a throttle valve opening (θTH) sensor 4.
And outputs an electric signal corresponding to the opening degree of the throttle valve 301 to supply it to an electronic control unit (hereinafter referred to as “ECU”) 5. This ECU 5
It constitutes a purge control means, a storage means, a purge start means and a purge stop means.

A fuel injection valve 6 is provided for each cylinder between the engine 1 and the throttle valve 301 and slightly upstream of an intake valve (not shown) of the intake pipe 2. The ECU 5 is electrically connected to the fuel tank 8 and electrically connected to the ECU 5, and the opening time of the fuel injection valve 6 is controlled by a signal from the ECU 5.

Immediately downstream of the throttle valve 301, an intake pipe absolute pressure (PBA) sensor 10 is provided via a pipe 9 and an absolute pressure signal converted into an electric signal by the absolute pressure sensor 10 is sent to the ECU 5. Supplied.

An engine speed (NE) sensor 11 is mounted around a camshaft (not shown) of the engine 1 or around a crankshaft, and a signal pulse (hereinafter referred to as "the pulse") at a predetermined crank angle position every time the crankshaft of the engine 1 rotates 180 degrees. A TDC signal pulse is output to the ECU 5.

O ₂ sensor 1 as exhaust gas concentration detector
Reference numeral 2 is attached to the exhaust pipe 13 of the engine 1, detects the oxygen concentration in the exhaust gas, outputs a signal corresponding to the concentration, and supplies the signal to the ECU 5.

A two-way valve 14 which constitutes a fuel vapor emission suppression device, a canister 15 containing an adsorbent 151, and a valve are driven between the upper portion of the sealed fuel tank 8 and the intake pipe 2 downstream of the throttle body 3. A purge control valve 16 which is a linear control valve (EPCV) having a solenoid that operates is provided. The solenoid of the purge control valve 16 is EC
The purge control valve 16 is connected to U5, and is controlled according to a signal from the ECU 5 to linearly change the valve opening amount. According to this fuel vapor emission suppression device, when the fuel vapor (fuel vapor) generated in the fuel tank 8 reaches a predetermined set pressure, it pushes open the positive pressure valve of the two-way valve 14 and flows into the canister 15. Adsorbent 151 in canister 15
Adsorbed and stored by The purge control valve 16 is EC
An on / off control signal (pulse signal) is supplied from U5,
The opening is controlled by changing the duty ratio of the control signal between 0 and 100%. In this embodiment, the duty ratio of 0% corresponds to the fully closed state, and the opening degree of the purge control valve 16 increases as the duty ratio increases. When the purge control valve 16 is opened, the fuel vapor temporarily stored in the canister 15 is purged together with the outside air sucked from the outside air intake 152 provided in the canister 15 by the negative pressure in the intake pipe 2. The air is sucked into the intake pipe 2 via the control valve 16 and sent to each cylinder. When the fuel tank 8 is cooled by the outside air and the negative pressure in the fuel tank increases, the negative pressure valve of the two-way valve 14 opens, and the fuel vapor temporarily stored in the canister 15 is returned to the fuel tank 8. It is. Thus, the fuel vapor generated in the fuel tank 8 is prevented from being released to the atmosphere.

An orifice 171 is provided on the purge control valve 16 side of the purge pipe 17 connecting the canister 15 and the purge control valve 16. Further, a pressure gauge 19 is provided on the purge pipe 17 between the orifice 171 and the purge control valve 16 via a pipe 18. The pressure gauge 19 and the orifice 171 constitute a differential pressure flow meter. The pressure gauge 19 is constituted by an atmospheric pressure differential pressure gauge. The pressure gauge 19 detects a relative pressure P1 in the purge pipe 17 with respect to the atmospheric pressure, and supplies a detection signal to the ECU 5. The differential pressure flow meter uses the jet area of the orifice 171 and the relative pressure P ₁ detected by the pressure gauge 19 to determine the flow rate (hereinafter, referred to as “purge flow rate”) QP 1 of the air-fuel mixture passing through the orifice 171 by the ECU 5 using the flow rate display value QS. Is calculated from

Further, the canister 15 and the orifice 17
A hot-wire flow meter (mass flow meter) 22 is provided in the purge pipe 17 between the first and second purge pipes 17 and supplies an output signal to the ECU 5 according to the flow rate of the air-fuel mixture including the fuel vapor flowing in the purge pipe 17. The hot wire type flow meter 22 utilizes the fact that when a heated platinum wire is exposed to an air current through an electric current, the platinum wire is deprived of heat and its temperature decreases, thereby reducing its electrical resistance.

The ECU 5 has an input circuit having functions of shaping the waveforms of input signals from various sensors, correcting a voltage level to a predetermined level, converting an analog signal value to a digital signal value, and the like, a purge control valve described later. A central processing circuit (hereinafter referred to as "CP
U)), various arithmetic programs to be executed by the CPU, storage means for storing a Ti map and a calculation result described later, an output circuit for supplying a drive signal to the fuel injection valve 6, the purge control valve 16, and the like. You.

The CPU determines various engine operating states such as a feedback control operating area and an open loop control operating area according to the oxygen concentration in the exhaust gas based on the engine operating parameter signals from the various sensors described above. According to the driving condition, based on the following equation (1),
The fuel injection time Tout of the fuel injection valve 6 is calculated in synchronization with the TDC signal pulse.

Tout = Ti × KO ₂ × K1 + K2 (1) Here, Ti is a reference value of the fuel injection time Tout of the fuel injection valve 6, and the engine speed NE and the intake pipe absolute pressure P
It is read from the Ti map set according to BA.

KO ₂ is an air-fuel ratio feedback correction coefficient, which is set in accordance with the oxygen concentration in the exhaust gas detected by the O ₂ sensor 12 during feedback control. In the area, the coefficient is set according to each operation area.

K1 and K2 are other correction coefficients and correction variables calculated in accordance with various engine operation parameter signals, respectively, for optimizing various characteristics such as fuel consumption characteristics and engine acceleration characteristics according to the engine operation state. Is set to a predetermined value.

The CPU supplies a drive signal for opening the fuel injection valve 6 to the fuel injection valve 6 via an output circuit based on the fuel injection time Tout obtained as described above.

FIG. 2 is a flowchart of a program for calculating a duty ratio DUTY, which is an opening control parameter of the purge control valve 16.

FIG. 2A is a flowchart of a program for calculating a DUTY value. In step S1, a vapor parameter X is read. The vapor parameter X is, for example, the DUTY value itself or the flow rate QP1 of the air-fuel mixture flowing through the purge pipe 17 or the flow rate of the fuel vapor (hereinafter referred to as “vapor flow rate”).
VQ) or the fuel vapor concentration (hereinafter referred to as “vapor concentration”) β in the air-fuel mixture. When these are not detected, the air-fuel ratio correction coefficient KO ₂ set based on the detection value of the O ₂ sensor 12 may be used.

Here, the vapor flow rate VQ is represented by a display value QS of a differential pressure flow meter comprising a pressure gauge 19 and an orifice 171;
It is calculated based on the display value QH of the hot wire flow meter 22. This is because when the vapor concentration β in the air-fuel mixture flowing through the purge pipe 17 changes, even if the purge flow rate QP1 is the same, Q
The calculation is based on the fact that the S value and the QH value change. Based on the QS value and the QH value, the vapor flow rate VQ is calculated.
In addition, the vapor concentration β and the purge flow rate QP1 can be calculated. Specifically, the detected QS value and Q
Based on the H value, for example, it is read from a map as shown in FIG. It should be noted that in FIG.
... is the purge flow rate QP1 (β = 0%
, QP1 = QS = QH), and the vapor flow rate VQ
Is obtained as QP1 × β.

In step S2, the vapor parameter X is compared with a reference value. This reference value is calculated based on the engine operating parameters (for example, engine speed NE, throttle valve opening θ).
TH etc.), and is set in consideration of preventing the average value of the air-fuel ratio correction coefficient KO ₂ from greatly deviating from 1.0 and deteriorating the responsiveness of the feedback control. As a result of the determination in step S2, when it is determined that the vapor flow rate VQ should be increased, the process proceeds to step S3, the DUTY value is increased by a predetermined amount, a limit check is performed (step S4), and the process proceeds to step S7. The limit check in step S4 is
When the DUTY value exceeds 100%, DUTY = 10
This is a process of setting 0%. On the other hand, if it is determined in step S2 that the vapor flow rate VQ should be reduced, the process proceeds to step S5, in which the DUTY value is reduced by a predetermined amount and a limit check is performed (step S2).
6), and proceed to step S7. In the limit check in step S5, when the DUTY value is smaller than 0%, the DUT
This is a process for setting Y = 0%.

In step S7, the DUTY value calculated in the above step is stored in a DUTY map. DUTY
The map is, for example, the engine speed NE at the time of calculating the DUTY value.
And a DUTY value corresponding to the intake pipe absolute pressure PBA.

FIG. 2B is a flowchart of a program for outputting a DUTY value.
It is determined whether or not the engine is in an operation state in which it is necessary to shift from a purge stop (off) state (purge control valve fully closed state) to a purge execution (on) state (purge control valve open state). If the answer is negative (NO), it is determined whether or not the engine is in the operating state to shift from the purge execution state to the purge stop state (step S12).

The answer in step S11 is affirmative (YES) or the answers in steps S11 and S12 are both negative (NO).
In other words, when the transition from purge off to on or when the purge on state is to be continued, the DUTY
The DUTY value stored in the map is read, and the DUTY
The control signal of the duty ratio corresponding to the value is supplied to the purge control valve 1
6 is output. When the answer to step S11 is negative (NO) and the answer to step S12 is affirmative (YES), that is, when it is necessary to shift from purge on to off, the DUTY value is immediately set to 0%, and the control signal having the duty ratio of 0% is purged. Output to the control valve 16.

According to the program shown in FIG. 2, the duty value is set as follows. That is, the vapor parameter X is gradually changed (by a predetermined amount) so as to coincide with the reference value during the execution of the purge, and is immediately set to the map storage value at the time of transition from the purge off to the on, and at the time of the transition from the purge on to the off. Immediately set to 0%. Therefore, it is possible to avoid the problem of gradually changing the opening degree of the purge control valve at the time of switching the purge on / off, to sufficiently exhibit the processing capability of the fuel vapor emission suppression device, and to improve the exhaust gas characteristics. .

In the above-described embodiment, the purge control valve opening is immediately changed at both the transition from the purge on to the off state and the transition from the off to the on state. May be gradually changed according to a normal control method.

[0034]

As described above, according to the present invention, the opening degree of the purge control valve is immediately changed to a desired value at the time of the transition from the stop of the purge to the execution and / or at the time of the transition from the execution of the purge to the stop. Therefore, it is possible to avoid the problem of gradually changing the opening degree of the purge control valve at the time of switching between the purge execution and the stop, to make full use of the processing capability of the fuel vapor emission suppression device, and to improve the exhaust gas characteristics. Can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an internal combustion engine and a control device thereof according to an embodiment of the present invention.

FIG. 2 is a flowchart of a program for calculating and outputting an opening control value (DUTY) of a purge control valve.

FIG. 3 is a diagram showing setting of a map referred to in the program of FIG. 2;

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 2 intake pipe 5 electronic control unit (ECU) 6 fuel injection valve 8 fuel tank 15 canister 16 purge control valve 17 purge pipe 19 pressure gauge 22 hot wire flow meter 171 orifice

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasujiro Tsutsumi 1-4-1 Chuo, Wako-shi, Saitama Pref. Honda Technical Research Institute Co., Ltd. (56) References JP-A-62-174557 (JP, A) 61-23644 (JP, Y2)

Claims (3)

(57) [Claims] A purge passage provided between a canister for adsorbing fuel vapor generated from a fuel tank and an engine intake system for purging an air-fuel mixture containing the fuel vapor;
A purge control valve for controlling the flow rate of fuel vapor supplied to the engine intake system through the purge passage; and a purge control valve for gradually increasing or decreasing the opening amount of the purge control valve. Control means, storage means for storing control parameter values of the purge control valve, and purge start means for setting the stored control parameter values as initial values at the start of purge supply from a purge stop state. Fuel control device for an internal combustion engine. 2. A purge passage provided between a canister for adsorbing fuel vapor generated from a fuel tank and an engine intake system and for purging an air-fuel mixture containing the fuel vapor,
A purge control valve for controlling the flow rate of fuel vapor supplied to the engine intake system through the purge passage; and a purge control valve for gradually increasing or decreasing the opening amount of the purge control valve. Control means, storage means for storing a control parameter value of the purge control valve, and purging stop for immediately setting the control parameter value to a value corresponding to the valve closing state when shifting from the purge supply state to the purge stop state And an evaporative fuel control device for an internal combustion engine. 3. The evaporative fuel control device for an internal combustion engine according to claim 2, further comprising a purge start unit that sets the stored control parameter value as an initial value when the purge supply is started from the purge stop state.